In existing systems implemented, for example, as part of a process for optical inspection of a surface of a substrate such a semiconductor (SC) thin wafer (700 micrometer and less) of circular shape, or as part of a SC Photolithography process, the wafer is attached to a supporting platform known as a “chuck”, For executing such a process, it is required to vertically move the chuck, for example, relative to an optical device, (or alternatively to move vertically the optical device), in order to adjust in local manner the distance of the wafer facing surface with respect to an optical device. Such systems implement an electro-mechanical and/or a piezoelectric adjusting mechanism in order to provide the focusing in a relatively high degree of accuracy, e.g., in a magnitude of up to very few nanometers. Such systems may also implement a mechanism, known as a “stepper”, to provide relative planer (XY) motion between the object and, for example, a stationary optical device. In many cases, the planer motion (scanning or point to point motion) required by the stepper may be very accurate in three-dimensional manner, e.g., in a magnitude of 10th and even few nanometers. Current systems implement linear motion, (for example, an accurate platforms that supports an linearly moves a thin (less than 1 mm), rectangular wide format Flat-Panel Display (FPD) that can be 6 m2 in area), rotational motion and/or planar (XY) motion of the object in order to provide the lateral relative motion between the facing surface of the object and the optical device. Thus, the focal distance below the optical device must be dynamically adjusted, at least locally, in conjunction with laterally moving the object.
Accordingly, the throughput of such systems may be related to the time response of the focusing mechanism and /or the time-response of the lateral motion mechanism. For example, a relatively heavy chuck, may result in a relatively slow time response.
A different problem of malfunctioning may occur if a sub-micron particle, having for example, a size of 0.5 micrometer or more trapped between a wafer and the chuck, e.g., when the wafer is clamped by the chuck, for example, by vacuum or electrostatic mechanisms. The particle may cause local distortion of the wafer facing surface, which may result in a critical failure of, for example, inspection or photolithography process. Such a particle may generate non-parallelism of local nature (small bump) such that the focusing mechanism may not be able to compensate such local wafer distortion.
Furthermore, contact between substrates (such as silicon wafer), and chucks may results with damage, e.g., by causing backside contamination and/or Electro Static Damage (ESD), or mechanical damage to the wafer.